Battered moon revealed

The scale of the battering the Moon received early in its history has been revealed in remarkable new data from two NASA satellites.

Mapping by Ebb and Flow - together known as the Grail mission - has shown the Moon's crust to be a mass of pulverised rock, the remains of countless impacts and far more extensive than previously thought.

Scientists say this is relevant to the study of the Earth's ancient past, because it too would have been pummelled in the first billion years of its existence by left-over debris from the construction of the planets.

Because the Earth's surface has been constantly remodelled by plate tectonics, all its early scars have long since healed.

"If you look at how highly cratered the Moon is - the Earth used to look like that; parts of Mars still do look like that," said Professor Maria Zuber, Grail's principal investigator from the Massachusetts Institute of Technology.

"This period of time when all these impacts where occurring - this was the time when the first microbes were developing.

"We had some idea from the chemistry (of ancient rocks) that Earth was a violent place early on, but now we now know it was an extremely difficult place energetically as well, and it shows just how tenacious life had to be to hang on," she told BBC News.

Professor Zuber was speaking at a meeting of the American Geophysical Union in San Francisco.